LED (light emitting diode) light sources are now calling attentions as next-generation new light sources. Unlike typical conventional light sources, LEDs do not use a filament and therefore have a long life. Further, LEDs have a number of advantageous features such as compact manufacturing due to its extremely small and thin dimensions. A wide range of lighting applications are expected for LEDs as light sources, with its favorable features including reduced limitations on the mounting position.
As one example, Japanese Laid-Open Patent Application No. S62-8403 discloses a lighting system that uses an LED light source formed by arranging linear lead frames in parallel, with each lead frame holding a plurality of through-hole type LED elements. Further, one technique is available for removably mounting such an LED light source as a “card-type LED module”. The “card-type LED module” is formed by arranging, instead of the lead wires, surface-mounting-type LED elements in parallel on a card-type substrate. This technique enables, on a main substrate where the socket is placed, various card-type LED modules each differing in color and illuminance of emitted light to be selectively mounted depending on the situation.
A card-type LED module formed by mounting a large number of LED bare chips on a metal base substrate has recently been developed. This card-type LED module is expected to have a higher illuminance by future research and development efforts in improving the luminous efficiency of LED bare chips, improving the packing density, and the like.
As one example, such a card-type LED module can be used as a light source for a lighting system by fixing the LED module to a lighting system 2000 using a socket 2020, according to a prior art technique shown in FIG. 16.
The lighting system 2000 shown in FIG. 16 is roughly composed of a base 2001 to be screwed into a socket designed for general-purpose incandescent lamps, and a case 2002 on which a card-type LED module (LED card 1000) can be mounted.
The case 2002 has the socket 2020 for holding the LED card 1000, at its bottom surface facing the surface where the base 2001 is attached.
The socket 2020 has grooves 2021 in which side parts 1000a and 1000b of the LED card 1000 can be engaged. The user mounts the LED card 1000 by inserting the side parts 1000a and 1000b of the LED card 1000 into the grooves 2021 of the socket 2020, and sliding the LED card 1000 from the peripheral part to the central part of the socket 2020. In lighting systems, a light source is usually to be positioned at the center. In the lighting system 2000 with the above-described construction, therefore, the LED card 1000 is to be slid to a predetermined position along the grooves 2021 of the socket 2020, so that the LED card 1000 as its light source is positioned at the center.
The LED light sources for lighting applications will be required to have a higher illuminance in the future. To meet such a requirement, efforts are being made toward higher integration of LEDs and a larger driving current for the LEDs. These efforts are encountered with the following problem.
The higher integration and larger driving current can increase an amount of light emitted by an LED light source. In proportion to the increase, an amount of heat generated in the LED light source also increases. It is generally recognized that an amount of heat generated in the LED light source is relatively small as compared with other typical light sources, but an amount of heat generated in such a card-type LED having a construction where a large number of LED elements are integrated is beyond a negligible level. With serving as a light source for lighting applications, LEDs included in the LED light source may be required to be lit for long hours. The amount of heat generated in the LEDs is inevitably large. In particular, an illuminance of light emitted from LEDs depends on their temperature characteristics. This means that some LEDs may fail to produce a desired illuminance under high-temperature conditions. Also, a plurality of LEDs of different colors may have different temperature characteristics. If these LEDs having different temperature characteristics are, combined for use as a light source, controlling of color emitted from the light source becomes difficult.
When a card-type LED module is inserted into a socket, heat generated from each LED included in the card-type LED module is trapped in the vicinity of the socket. Such significant concentration of heat in one area is problematic. In view of this, a card-type LED module is required to have good heat-releasing properties.
This requirement for good heat-releasing properties also applies to the lighting system 2000 shown in FIG. 16. To be specific, the LED card 1000 is also required to have further improved heat-releasing properties when the socket 2020 described above is used.
Another problem to be solved is a difficulty in the replacement operation of the LED card 1000.
To remove the LED card 1000 from the lighting system 2000 for such reasons as its life being expired, the user is required to slide the LED card 1000 along the grooves 2021 from the central part toward the peripheral part of the case 2002. This removing operation can be difficult for the user because the lighting system 2000 is often placed in an area of limited accessibility such as on the ceiling. In particular, if the user tries to remove the LED card 1000 by uncomfortable body positioning such as stretching his or her arms or bending his or her body, the side parts 1000a and 1000b of the LED card 1000 may get stuck in the grooves 2021, thereby increasing the burden on the user involved in the replacement operation. Accordingly, the lighting system 2000 needs to be improved to enable an easy replacement operation of the LED card 1000.
In the lighting system 2000, a longer distance by which the LED card 1000 is to be slid from the central part toward the peripheral part of the case 2002 not only makes the replacement operation difficult as described above, but also degrades the appearance of the lighting system, with its construction being such that the grooves 2021 extend from the light source unit to the peripheral part of the case 2002.
To solve this problem, the lighting system may be constructed such that the socket 2020 is projected from the surface of the case 2002 so that the LED card 1000 can be placed at such a position that allows easy access by the user. In this case, however, the projected part may drastically degrade the appearance of the lighting system. For the lighting system 2000, a recessed part may be formed in the surface of the case 2002, and the socket 2020 may be placed in the recessed part, so that the socket 2020 holding the LED card 1000 is not projected. However, simply employing such a constructing may further complicate the replacement operation of the LED card 1000.
As described above, sockets designed for card-type LED modules for practical use and lighting systems using the LED modules as light sources still require improvements.